While we usually wait for a Progress Report to write about bug fixes and other features, a regression was causing so many issues that we've decided to roll out an early monthly build and detail what happened and why right now. If you're a heavy of Dolphin's through features, this is a rather important update.

libusb Thread Safety Problems¶ 366x6e

libusb is an incredibly powerful library that facilitates direct communication to USB devices without needing to develop a kernel level driver. It also has the benefit of being cross platform between Windows, Linux, macOS, and even FreeBSD! Last Month, we saw a tremendous update to through that fixed many issues on Dolphin's side and libusb's side, resulting in greater compatibility and stability among devices.

Unfortunately, things managed to break in another way due to some changes made to how Dolphin handles through. Pretty much anyone on Windows using any sort of through could potentially trigger one of the following issues, and it got particularly bad when multiple types of through were combined.

• Using multiple libusb devices at once, such as Bluetooth through and GameCube Controller through at the same time.
• Reinitializing a libusb device during one session, such as booting multiple games rapidly or playing a game that uses ES_Launch
• Other unknown combinations involving USB through and BlueTooth through/GameCube Controller through

If any of these conditions were triggered, Dolphin would usually crash. Sometimes, Dolphin could lock up and close without crashing, resulting in a ghost instance that would block any further instances of Dolphin from being able to use through features until the force closed the locked up instance. What caused this serious regression?

The problem stems from a change to how Dolphin handled each type of through. With the latest batch of changes, Dolphin would use a single context for GameCube Controller through, Bluetooth through, and USB through. This was meant to simplify code and help accomodate usbdk s as it became unstable when we were using multiple contexts. In theory, everything should have been fine, as libusb was documented to be threadsafe in the situations we were going to be using it.

Unfortunately, this documentation is incorrect or we're misunderstanding it. While things weren't obviously wrong in isolated testing of each individual feature, it turns out that libusb would consistently deadlock when calling synchronous functions from multiple threads. The most common way to trigger this was by using two forms of through at the same time. After over a week of investigation, we still have no idea if the fault is on our understanding of how libusb is supposed to work or a bug in libusb itself. Because we can't leave Dolphin in this state, we've decided to revert back to using multiple contexts and drop usbdk .

We apologize to the sudden change in course, but this is a necessary step in providing a stable experience. These regressions, and subsequent fixes, should only affect s on Windows. At this point, we still recommend the libusbK driver, though, the WinUSB driver will also work for most devices. If you were already using one off those two drivers, you do not need to change anything, just update to the latest builds and the instability should be fixed. It is highly recommended that usbdk driver s uninstall the driver and switch to libusbK or winUSB.

If you need to change drivers, or even want to try through for the first time, we have updated the guides for GameCube Controller through, Bluetooth through, and USB through